1. Field of the Invention
This invention relates generally to information record discs and, more particularly, is directed to an information record disc for use in recording video information signals, for example, for still-picture reproduction.
2. Description of the Prior Art
An information record disc has previously been used for recording video information signals in a video camera in a plurality, for example, twenty-five, spiral tracks thereon, with one field of video signals being recorded in each track and one field of a still-picture being reproduced by scanning each track. In this regard, during recording and reproducing from the record disc, a magnetic head contacts the disc when the latter is positioned and rotates within a magnetic recording apparatus.
In accordance with the aforementioned prior art information record disc, a central core made of plastic or other similarly deformable material includes a central bore and an outer flange to which a magnetic disc is adhered. An annular yoke having a central bore and made of a magnetic material, for example, permalloy or the like, is secured to the central core at the underside thereof. During operation, the yoke is attracted by a magnet of the magnetic recording apparatus so as to position the record disc at a predetermined position therein. At such time, a projection or spindle from the magnetic recording apparatus projects through the central bores of the yoke and core and a lower circular skirt of the core also contributes to positioning the record disc in the magnetic recording apparatus.
However, with such prior art arrangement, because the central core is made of plastic which has a high thermal expansion coefficient, the configuration of the central core changes in accordance with temperature changes. In such case, the configuration of the outer flange thereof which has a relatively small thickness undergoes relatively large transformations, resulting in buckling of the magnetic disc which is adhered to the surface of the outer flange. This, of course, results in unstable contact of the magnetic recording head with the magnetic disc, resulting in deterioration of the recording operation. Further, since the yoke is adhered to the underside of the core by an adhesive, the time required to assemble the central core and yoke together may be relatively long, and the strength of contact between the central core and yoke varies with the type of adhesive utilized.